The purpose of this research study is to find out: 1) Is raloxifene, also known by the trade name Evista, effective in reducing the incidence of breast cancer in women who are at increased risk for developing cancer? 2) If it is effective, how does raloxifene compare to tamoxifen, also known as Nolvadex, in reducing the incidence of breast cancer? 3) How do the side effects (good and bad) of raloxifene and tamoxifen compare?